The present invention relates in general to an unlimited sliding ball bearing spline assembly which includes a ball bearing and a spline shaft slideably supported by the ball bearing and which allows linear relative motion between the ball bearing and the spline shaft singly or in combination with transmission of torque from the spline shaft to the ball bearing or vice versa.
The ball bearing spline assembly which the present invention concerns enjoys wide application on spindles of various machine tools, columns and arms of industrial robots, auto-loaders, spindles for spot welding machines, guide shafts for various high-speed automatic machines and others.
The unlimited sliding ball bearing spline assemblies of the type mentioned above have heretofore been known. In general, the ball bearing of the ball bearing spline assembly is composed of an outer sleeve and a cage for holding therebetween a large number of balls grouped into a plurality of sets in each of which balls are guided as load carrying and no-load carrying balls along an elongated loop-like raceway formed in substantially U-like grooves. These grooves are formed in the wall and an inner peripheral surface of a cylindrical outer sleeve of a steel material, which involves complicated and expensive machine processings. For example, preparation of the outer sleeve requires a turning work, while formation of the various longitudinal grooves requires a broaching work. A relatively large number of steps for these machine processings of different types provides a major cause for increasing the costs of the finished products.
Further, the cage which is fitted within the outer sleeve is usually formed by pressing working and composed of a plurality of segments longitudinally extending and uniformly destributed in the circumferential direction of the outer sleeve and requires much complicated and troublesome procedures upon assembling, giving rise to a possibility that the smooth relative displacement between the spline shaft and the ball bearing could not be attained due to errors possibly involved in the assembling.
Besides, since a rolling direction changing groove for transferring the balls from the load-carrying ball zone to the no-load carrying ball zone or vice versa is located at a joint portion between the outer sleeve and/or the cage and an end cover plate, even a slight offset produced at the joint portion provides resistance to the smooth rolling of the balls and/or a cause for generation of noise.
Besides, because of such an arrangement that a line passing the axial center of the outer sleeve and the center of the load carrying ball intersects at an obtuse angle a line which passes the load carrying ball and the no-load carrying ball, a considerably great radial distance is produced between the axial center of the outer sleeve and the center of the no-load carrying ball, thereby giving rise to a problem that the circulatory movement of the balls encounters difficulty under the influence of a centrifugal force to which the balls are subjected upon rotation of the ball bearing spline assembly.